1. Field of the Invention
The present invention relates to the intimate contacting or admixture of a plurality of physically distinct phases, at least one of which being a gaseous phase, and plural phase oontactor therefor. The invention is especially well adapted for various drying operations.
2. Description of the Prior Art
In copending application, Ser. No. 916,477, filed June 19, 1978 (now abandoned), a continuation of Ser. No. 770,802, filed Apr. 19, 1977 (now abandoned), which itself is a continuation of Ser. No. 479,774, filed June 17, 1974 (also now abandoned), all assigned to the assignee hereof, there is disclosed and claimed novel means for the intimate contacting of a plurality of physically disparate phases, at least one of which being a gaseous phase, which may comprise solid or liquid particulates, and with another phase being dispersible therein, e.g., a liquid, solution or suspension phase, or optionally a solids phase, such as a powder.
The process disclosed in the aforesaid '477 application features the intimate contacting of substances which are in different phases, at least one of which is in a gaseous or vapor phase with or without entrained solids in solution or dispersion comprising:
(i) introducing said phase into a flow of helical paths which are symmetrical with respect to a plane passing through the axis of flow; PA1 (ii) passing said symmetrical flow through a restricted passage of circular cross-section having its center along the axis of the symmetrical helical flow; PA1 (iii) allowing said flow of said phase to pass through said restricted passage into a circular space whereby the path of movement of said phase following passage through the restricted opening is in the form of layered stacks of a plurality of hyperboloids; PA1 (iv) introducing a fluid as a liquid stream in rectilinear flow through the restricted passage along the axis of helicoidal flow, with said liquid stream being introduced through a conduit spaced from the plane of the restricted flow passage of the helicoidal flow by a length which is between zero and the mean radius of said flow passage; and PA1 (v) imparting to the phase forming the helicoidal symmetrical flow a momentum at the level of the restricted passage of at least 100 times greater than the momentum of the fluid in rectilinear flow, whereby the fluid constituting the continuous rectilinear flow is broken up upon engagement with the phase in helicoidal flow into small particles which become entrained by the phase in helicoidal flow for movement therewith in the same direction and intensity.
Thus, a region of plug flow type is established, as from contact between the phases, producing regular and instantaneous treatment of the dispersible phase which generally constitutes the phase to be treated. The treatment is of flash type, namely, it is very short, and may be accompanied by a substantial difference in temperature between the phases.
The foregoing process enjoys many advantages and benefits, both from the point of view of granulometry, fineness and narrow range of distribution, and from the point of view of the treatment, homogeneity of treatment, from one particle to the other, and speed of treatment. It will be readily appreciated that the requirements involved in regard to actually carrying out the process are nonetheless very severe.
And said '477 copending application also describes and claims various means for producing the tangential movement, by introducing the gaseous phase tangentially with respect to the dispersible phase or by arranging a helicoidal strip or deflector vanes around a central pipe for guiding the dispersible phase.
However, a serious problem exists in the quality of the symmetry of the flow. It is for this reason that copending application, Ser. No. 916,477, also claims a multi-tangential distribution system comprising an annular space which is fed by way of at least one tangential inlet and which is delimited inwardly of the apparatus by a perforated wall, each perforation acting as a tangential inlet.
This apparatus provides flow of a sufficient quality, in many cases.
Unfortunately, it has been found that for some applications there result deposits of material adhering to the walls of the contact chamber.
It too has been proposed to overcome certain problems, including that of objectionable deposition of encrusting solids, by creating a cooling region at the level of the contact region, as described in U.S. Pat. No. 4,263,234, also assigned to the assignee hereof, and it has also been envisaged that the quality of flow may be improved by optimizing the various possible parameters of the apparatus, e.g., the shape of the holes, the physical arrangements, and the like.
It has been observed from experimentation that two parameters are important: the speed of rotation of the helicoidal flow and its speed of linear advance, the same being the "downward" movement, with the apparatus generally being positioned vertically. Indeed these factors vary depending upon the nature of the product to be treated, in fact in accordance with the rheology of the dispersible phase. It thus logically follows that, if it is to be satisfactory, any solution to the aforesaid problem must accommodate all variations in process parameters.
Also compare U.S. Pat. Nos. 3,758,081, 4,086,099, 4,124,353, 4,257,339, 4,265,702, 4,267,131 and 4,308,039, all assigned to the assignee hereof.